(a) Field of the Invention
This invention relates to novel compounds classified in the field of organic chemistry as 3-aryl-3-heteroarylphthalides and 3,3-bis (heteroaryl)phthalides useful as color precursors, particularly in the art of carbonless duplicating as, for example, in pressure-sensitive systems, in thermal marking systems and in hectographic or spirit-reproducing copying systems; to substituted 2-(indolylcarbonyl) benzoic acids and 2-(pyrrolylcarbonyl) benzoic acids useful as intermediates to the subject phthalide color precursors; to processes for preparing said phthalides and benzoic acids; and to pressure-sensitive duplicating systems, thermal marking systems and hectographic copying systems containing the same.
(b) Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for carbonless duplicating systems. Among the more important classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides with which this invention is concerned, for example, crystal violet lactone; fluorans, for example, 2'-anilino-6'-diethylaminofluran and 2'-dibenzylamino-6'-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289 which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art suffer one or more disadvantage such as low tinctorial strength, poor light stability, low resistance to sublimation, low susceptibility to copiability of the color-developed form in standard copying machines, for example, a Xerox copier, and low solubility in common organic solvents, the latter disadvantage thus requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 3,491,112, issued Jan. 20, 1970 discloses in most pertinent part of series of normally colorless phthalides stated to be useful as color formers in pressure-sensitive copying paper which are represented by the structural formula ##STR1## wherein
is a heterocyclic radical selected from the group consisting of ##STR2## in which R.sub.1 and R.sub.2 are C.sub.1 to C.sub.4 alkyl, phenyl and hydrogen; Z and Y are hydrogen and dialkylamino in which alkyl is C.sub.1 to C.sub.4 alkyl with the proviso that only one Z and Y can be said dialkylamino while the other is hydrogen; and R.sub.3 and R.sub.4 are C.sub.1 to C.sub.4 alkyl.
U.S. Pat. No. 3,779,753, issued Dec. 18, 1973 discloses the phthalide having the formula ##STR3## which is stated to be useful as an optical filter agent in photographic processes to protect a selectively exposed photosensitive material from further exposure during processing in the presence of incident light.
British Patent Specification No. 1,427,318, published Mar. 10, 1976, discloses the interaction of trimellitic anhydride and m-diethylaminophenol to obtain a mixture of 4-diethylamino-2-hydroxybenzophenone-2', 4' -dicarboxylic acid and the corresponding 2', 5'-dicarboxylic acid isomer. The isomeric mixture is then interacted with 3,5-dimethylphenol in the presence of sulfuric acid followed by treatment with sodium hydroxide to obtain the compound having the structure ##STR4## which is stated to be useful as a color former in a spirit reproducing process.
U.S. Pat. No. 3,509,174, issued Apr. 28, 1970, discloses 1,2-dimethyl-3-(2-carboxybenzoyl)indole which is stated to be an intermediate to a series of 3,3-bis (3-indolyl)phthalides useful as color formers in pressure-sensitive copying paper.